1. Field of the Invention
The present invention generally relates to mechanical loading devices of the type employed to raise, transport, and lower workpieces in a manufacturing setting. More specifically, this invention relates to a mechanical loading device capable of producing a substantially rectilinear output motion from a rotational input, such that the output motion is reversible and can be controllably accelerated and decelerated as desired.
2. Description of the Prior Art
Mechanical loaders are widely used in manufacturing to move workpieces between work stations, and to and from conveyor belts. Generally, such mechanical loaders must be capable of a substantially rectilinear output motion which includes a vertical movement in order to clear the surfaces on which the workpieces are positioned, and a horizontal movement during which the workpieces are transferred from one station to the next. While significant variations in the precise output motion required can exist, many mechanical loaders rely on a rotational input from which their rectilinear output motion is derived. As one would expect, the availability of electric motors capable of being accurately controlled in forward and reverse directions makes rotational input to mechanical loaders highly desirable.
Apart from these general characteristics noted above, numerous mechanical loader designs are known and available in the prior art. One such example is U.S. Pat. No. 4,137,797 to Brems. Brems teaches a prime mover mechanism which generates a substantially square output motion from a rotational input. To do so, Brems relies on a planetary gear system in which an eccentric shaft extending from a planet gear provides the desired rectilinear motion. The eccentric shaft exhibits four distinct acceleration-deceleration cycles as it proceeds along its square output path due to the rotation of the planet gear relative to the frame.
While the device taught by Brems is capable of efficiently producing a rectilinear output motion from a rotational input motion, a disadvantage with the device is the reliance on a planetary gear system to transform the rotational input to the rectilinear output. As a result, a large mass must be rotated in a manner that may create significant eccentric loads. The inertial mass of the planetary gear system also tends to make it difficult to quickly pause the device in midmotion, a requirement which arises if only a portion of the square output motion is required to properly transport a workpiece to and from a station. Finally, the output motion produced by the eccentric shaft does not extend laterally beyond the perimeter of the device's structure, such that the device may require excessive floor space in order to suitably transport a workpiece between work stations.
A loading device which is specifically structured to produce a rectilinear output motion consisting of a lift, transport and lower movement is taught in U.S. Pat. No. 4,400,984 to Ronbeck. Contrary to Brems, Ronbeck relies on a parallelogram linkage arrangement in order to produce the desired rectilinear output motion. As such, the loading device taught by Ronbeck is capable of generating the desired output motion outside of its main structure, and further has the potential for being lighter in weight and easier to maintain than the planetary gear system of Brems. However, Ronbeck utilizes an air cylinder as the input device by which a crank is pivoted to produce the rectilinear output motion of the loading device, such that the overall structural and handling capabilities of the loading device are somewhat limited by the nature of the air cylinder, and the degree to which it can be accurately controlled.
From the above discussion, it can be appreciated that the prior art teaches diverse mechanisms by which a rectilinear output motion is generated that can be utilized to load and unload workpieces from a work station. However, it can also be appreciated that certain desirable characteristics, such as precision and control of the motion, and compactness and maintainability of the device are somewhat difficult to achieve within a single mechanism. More specifically, it would be desirable to provide a mechanical loader which is more compact so as to minimize the floor space required to accommodate it, readily maintainable in order to promote reliability and a long service life, and offers a highly controllable output such that workpieces can be accurately transferred between stations in order to enhance throughput and the overall efficiency of the manufacturing process.
Accordingly, what is needed is a cost-efficient, compact and readily maintainable mechanical loading device whose output is characterized by a precision rectilinear motion that is generated by a rotational input motion, the mechanical loading device providing a rigid transfer structure capable of handling large workpieces.